With the progress of science and technology, the operating system (OS) of the current computer system is able to support the touch screen technology. Recently, the touch screen gradually replaces the conventional mouse to control the computer system. By making a gesture on the touch screen with one or more fingers, an action of zooming, rotating or translating a target item may be correspondingly performed.
FIGS. 1A and 1B schematically illustrate an action of zooming in a target item of the computer system in response to a gesture on the touch screen. A toolbar 110 of the operating system is shown on the touch screen 100 of the computer system. The toolbar 110 has several user interfaces, for example including a start button 112 and a network status icon 114. In addition, a window of an application program 120 is shown on the touch screen 100, and a first image 160a is shown on a workspace of the application program 120. The workspace is an area of the window of the application program 120 for allowing the user to perform the action of zooming, rotating or translating the first image 160a. 
In a case that the user wants to zoom in the first image 160a of the workspace, two touch points 150 and 155 are placed on the workspace of the application program 120 shown on the touch screen 100, then the two touch points 150 and 155 are moved away from each other, so that the distance between two touch points 150 and 155 is increased (see FIG. 1A). After the two touch points 150 and 155 are departed from the touch screen 100, a second image 160b is shown on the workspace of the application program window 120 (see FIG. 1B). Therefore, the first image 160a is enlarged as the second image 160b by the application program 120 in response to the gesture of the user.
Whereas, in a case that the user wants to zoom out the first image 160a, the two touch points 150 and 155 are moved toward each other, so that the distance between two touch points 150 and 155 is decreased. After the two touch points 150 and 155 are departed from the touch screen 100, the purpose of zooming out the first image 160a is achieved. Similarly the action of rotating or translating the first image 160a may be performed by changing the relationship between the two touch points in response to a specified gesture of the user. Moreover, the specified gesture of the user is defined by the manufacturer of the computer system.
The computer system has a touch screen signal processing device for recognizing the gesture of the user according to the touch points of the user. By the touch screen signal processing device, the computer system may execute a corresponding command in response to the gesture of the user.
FIG. 2 is a schematic functional block diagram illustrating the architecture of a touch screen signal processing device used in the conventional computer system with a touch screen. As shown in FIG. 2, the touch screen signal processing device comprises a touch unit 300, a gesture engine 304, and an application program 310. The touch unit 300 comprises a touch screen 301 and a driver 302. The gesture engine 304 is used for receiving a position signal from the touch unit 300. In response to the position signal, the gesture engine 304 issues a gesture event to the application program 310 through an application program interface (API) 320. According to the gesture event, the application program 310 executes a corresponding action.
In a case that multi-touch points are generated on the touch screen 301, the driver 302 generates a corresponding position signal. The position signal may be a coordinate signal. Moreover, according to a change of the position signal, the gesture engine 304 recognizes a gesture of the user and thus issues a corresponding gesture event to the application program 310.
Although most of the gesture-based application programs can process the gesture event, these application programs fail to smoothly perform the zooming action, the rotating action or the translating action. Under this circumstance, the effect of the gesture is discontinuously expressed. Therefore, user may experience the screen lag during the operation, since response of the application program is slow.
FIG. 3A schematically illustrates the trajectories of two touch points during a zooming-in action is performed in the conventional computer system. During the zooming-in action is performed, a first position signal 610 and a second position signal 620 corresponding to the trajectories of two touch points are continuously transmitted from the touch unit 300 to the gesture engine 304. As shown in FIG. 3A, the two touch points appear at the time spot t0, and the two touch points disappear after the time spot t3.
For realizing the type and function of the gesture of the user, the gesture engine 304 recognizes the position signals during the time interval T1 between the time spot t0 and the time spot t1, thereby generating a first zoom gesture event to the application program 310 at the time spot t1. After the first zoom gesture event is generated, the identical type of zoom gesture event is periodically generated in every time interval T2. That is, after the first zoom gesture event is generated, the gesture engine 304 generates a second zoom gesture event to the application program 310 at the time spot t2. Moreover, after the second zoom gesture event is generated, the gesture engine 304 generates a third zoom gesture event to the application program 310 at the time spot t3. According to the first zoom gesture event, the second zoom gesture event and the third zoom gesture event, the content of the workspace is correspondingly enlarged.
Experiments demonstrate that the time interval T1 is about 1.3 second and the time interval T2 is about 0.7 second. For most gesture-based application programs, the effect of the gesture is discontinuously expressed when the number of the received zoom gesture events or the accumulated change amount of the zoom gesture event match a specified value. Consequently, from the time spot t0 to the time spot t3, the user may feel that the image is not smoothly and continuously enlarged (see FIG. 3B).